Perfluoroelastomers have long been used in a variety of applications that require excellent resistance to high temperature and chemical attack. One particularly outstanding fluoropolymer that has been used in elastomeric applications is that prepared from tetrafluoroethylene (TFE) and perfluoro (alkyl vinyl) ether, and particularly perfluro (methyl vinyl) ether (PMVE) To facilitate the crosslinking in these copolymers that is essential to good elastomeric properties, a small percentage of termonomer is generally incorporated, such as the cyano-containing fluoroolefins described in Breazeale, U.S. Pat. No. 4,281,092.
While these cyano-perfluoroelastomers have exhibited outstanding thermal and oxidative stability, continuing effort has been directed to further modification of these polymers to broaden the areas in which they can be used. Particular attention has been paid to the rate and thoroughness of the curing reaction that has been used with perfluoroelastomers. Specifically, the perfluoropolymers previously made from TFE, PMVE and a cure site monomer typically exhibit a high concentration of ionic end groups, such as carboxylic or sulfonic acid moieties, which are introducted from the initiating system. Conventional chain transfer agents can be used to lower the concentration of the ionic end groups and also lower the polymer viscosity. However, the physical properties of these polymers are generally depreciated with such chain transfer agents.